S A fake station is used to detect a subscriber identity. This procedure may be called IMSI catching. However, in recent mobile phone systems (5G) the subscriber identity is encrypted, whereby traditional detection methods do not work.
IMSI catching of LTE, UMTS and GSM mobile subscriber apparatuses is possible using a fake base station because LTE/UMTS/GSM mobile subscriber apparatuses respond to an identity request (IMSI) message sent by a fake base station. This approach is not possible for 5G mobile subscriber apparatuses because 3GPP standards prevent it. For example, the latest 5G NAS specification 24.501 v1.1.1 defines clearly that only IDENTITY REQUEST with SUCI is possible before integrity protection is activated. The 5G mobile subscriber apparatuses send always SUCI (Subscription Concealed identifier) which is encrypted, and, cannot be used to find out the subscriber identity.